Friday, April 3, 2015

This is the site of the seasonal Fish Lake. And no, it doesn't look much like a lake to me, either. But winter and spring runoff from the Western Cascades backs up behind the barrier of the young lava flows shown over the previous days, and creates a temporary standing pool. That water slowly drains into the basalt breccia, and drains the lake by early to mid-summer. Prior to last fall, I had never bothered to stop at what looked to me like a meadow mislabeled as a lake, but prior to Ann Jefferson's visit in 2013, I'd not thought too much about the amazing hydrology of this area.

The peak in the distance is Iron Mountian.

Now, the most interesting information I learned here was contained in a sign, which I stupidly didn't think to photograph. Fortunately, some other, smarter, soul did think to photograph it and post it on the interwebz. The text reads,

You are standing on the shore of a lake that may seem old but in geologic terms was formed yesterday. Fish lake continues to change, seasonally and through the decades

Around three thousand years ago an eruption of Nash Crater formed Fish Lake by damming Hackleman Creek. Seasonal rains and snow overwhelm this little valley’s ability to drain the inflow so that each winter a lake is formed. In the summer, after the last snow melts off the ridges overlooking the valley, the lake quickly disappears and Hackleman Creek vanishes into the lava lakebed.

Grasses that have adapted to the seasonal drying of Fish Lake quickly transform the lake into a lush meadow. The local Hackleman trout [a subspecies of cutthroat trout] population has adapted to this seasonal disappearance of their lake home. When the temperature of the lake starts to rise, the trout head upstream into the creek where they wait for the arrival of winter and the lake’s return.

During times of especially heavy runoff, there is an overland channel from this basin to Clear Lake, but for the most part, the trout in this drainage are reproductively isolated from those lower down in Clear Lake and the McKenzie River. The fact that the subspecies has its own name suggests that evolutionary divergence may be occurring, though I don't know enough to make that claim with any confidence.